Hydraulic A-Frame on Ship with Polymer Bearings Provides Maximum Freedom of Movement

May 25, 2022 Mark McGwin

Hydraulic A-Frame with maximum freedom of movement

The Linkage System gives the A-Frame made by Ship & Yacht Engineering a 180-degree range of motion

Founded in 2000, Ship & Yacht Engineering Limited specializes in managing and implementing complex shipbuilding and marine technology projects. Its founder and CEO, Erik Hofmann, develops everything needed in shipbuilding, from ramps to cruise ships. While working with various shipping companies, he continually became aware of the disadvantages of A-Frames. He then developed an A-Frame with maintenance-free, self-lubricating pivot kinematics for a 180-degree motion radius: the Linkage System. To minimize maintenance and keep the kinematics bearing points free of lubrication, Hofmann uses iglide® plain bearings.

Hofmann's unique A-Frame stands in the port of Leer in East Frisia. At first glance, it is not unlike traditional A-Frames. However, closer examination reveals one crucial difference. Unlike other hydraulically operated A-Frames, this one has no external cylinders. This is the great advantage of Hofmann's innovation. The lifting system is tilted with the Linkage System. The cylinders and the unique pivot kinematics are installed in the A-Frame's structure, allowing a motion radius of 180 degrees.

"Conventional A-Frames have external hydraulic cylinders that severely restrict motion radius," Hofmann explains. "This makes operations such as hooking up a heavy pulley at sea complicated and dangerous for the crew."

A rope hoist provides A-Frames with a simple mechanism but also limits their motion radius. Designing an A-Frame with the largest possible range of motion requires great effort. Distances, the height of the rope, and the hoist structure all contribute to ensuring the largest possible radius.

Suitable for up to 20 tons of pivot load

The Ship & Yacht Engineering A-Frame has already been approved by the classification society and can lift loads of up to 20 tons, depending on pivoting angle (Picture UR0322-2). It is now being installed on a research vessel belonging to Fugro, the world's leading geodata specialist, where it will be used to place magnetometers into the water and pull them out again.

To ensure that the pivot kinematics operates without problems on the high seas and under harsh weather conditions, Hofmann was looking for self-lubricating, maintenance-free plain bearings that were also cost-effective. He had previously used bronze bushings. However, as weather conditions constantly flushed grease out of the bearings, fresh grease must be continually applied to ensure sufficient lubrication and prevent corrosion.

Self-lubricating effect prevents a lack of lubrication

A recommendation made Hofmann aware of igus GmbH, a developer and manufacturer of self-lubricating, high-performance plastics in Cologne, Germany. The company's plain bearings made of the material iglide TX1 are now used in the A-Frame's pivot kinematics (Picture UR0322-3). The igus bearings minimize maintenance and require no lubrication, and have been developed explicitly for high-load applications.

"Our plain bearings incorporate a solid lubricant, enclosed in millions of tiny chambers within the material," explains Uwe Sund, Product Manager for iglide Heavy-Duty Bearings. "That way, sufficient lubricant is available to lubricate the bearing point. So, there is always lubrication."